Gravity Field
Topography
Ge193, Special Topics in Geophysics: Tectonics of the South Atlantic Ocean. 3 units (1-0-2).
Instructors: Joann Stock, Rob Clayton
This course is offered in Winter Term, 2001. It is preparation for the course Ge211 in Spring Term 2001 which will involve field work on a geophysics research vessel. Ge193 will meet one hour a week to discuss papers related to the study area.
Our class will meet weekly in 212 North Mudd. Our final 2 meetings are scheduled to be as follows: Wed. Feb. 28th from 10-11 a.m.; Thurs. March 8th from 11-12 in the morning.
Scientific objectives of transit NBP 01-02 (Capetown to Punta Arenas).
The transit NBP01-02 in April 2001 (from Capetown to Punta Arenas) will allow us to collect some data in a little-studied area of the South Atlantic Ocean, on either side of the Falkland-Agulhas Fracture Zone. There are two problems of interest in this region: 1) an apparent magmatic ridge east of the ridge axis south of the Falkland-Agulhas FZ; and 2) the general fit of the magnetic anomalies, particularly chrons 20 and older, near the Falkland-Agulhas FZ.
Plate reconstructions in this region describe the history of displacement between the South America, Africa, and Antarctica plates (Shaw and Cande, 1990; Cande et al., 1988). These reconstructions were done over 10 years ago and using only the first pass of satellite gravity data to define the fracture zones. These reconstructions fit well the data north of the Antarctica-South America- Africa triple junction (the Bouvet T.J.) back to chron 13 time, and fit well the data north of the Falkland-Agulhas FZ for older times. Prior to chron 27 the spreading center south of the Falkland-Agulhas FZ much farther east and a different pole of opening. There is a dead spreading center preserved between the Meteor Rise and the Agulhas Plateau, whose magnetic anomalies (from chron 34 to chron 27) recorded motion between Africa and a Malvinas microplate rather than between Africa and the South America plate (Marks and Stock, 1998; LaBrecque and Hayes, 1979).
The published reconstructions for chron 27 to chron 13 for South America and Africa do not fit well the limited data near the southern end of the plate boundary (at and south of the Falkland-Agulhas FZ). The sense of misfit is such as to misalign the fracture zones with their conjugates, while still matching well the magnetic anomaly picks from both plates. This amount of misfit could be within the errors of the reconstructions, because few data were available in this region at the time the reconstructions were done. Alternatively, the presence of this misfit could indicate that the plate motion scenario was more complicated, with independent motion of the southern part of one of the plates (South America or Africa) compared to their motions to the north.
On Palmer 01-02 we will collect a flow line with magnetics, gravity, and SeaBeam data north of the Falkland-Agulhas Fracture Zone, with a minor deviation to study a magmatic ridge south of the Falkland-Agulhas Fracture Zone. These studies will help us to address this question.
Click here to see the list of references for the class.
Last updated: February 22, 2001.
